1. Field of the Invention
This invention relates to electric steam boilers, and particularly to electrode boilers for use with "dirty" water.
2. Description of the Prior Art
In immersion type electrode boilers, electrodes connected to an appropriate source of electrical power are either completely or partially immersed within an electrolyte to be heated to produce steam or otherwise to employ the heat so generated. The electrical current density at the electrode surfaces must be kept below that at which unacceptable electrochemical corrosion would occur. As electrical conductivity of the electrolyte employed increases (e.g., by use of high conductivity "dirty" water), electrical resistance to electrical current flow decreases, so that for given voltage the current density within the electrolyte, and consequently the electrical current density at the electrode surfaces, increases. The maximum current density tolerable by the material, e.g., stainless steel, of conventional immersion type boiler electrodes requires use of purified water, or at least water having a conductivity no greater than a certain predetermined level.
Prior art techniques for accommodating high conductivity water include that described in U.S. patent application Ser. No. 32,116, filed Apr. 23, 1979 by T.A. Keim and my earlier-filed U.S. patents application Ser. No. 34,373, filed Apr. 30, 1979, both assigned to the instant assignee, and both incorporated herein by reference. Each of the above-mentioned U.S. patent applications describes a system employing insulators to maintain electrical resistance regardless of water conductivity at such a level that the current density between the electrodes remains at acceptable values to limit electrode corrosion. The above-cited application Ser. No. 32,116 discloses a system employing an insulating wall having fluid flow paths therethrough. The above-cited application Ser. No. 34,373 discloses a system employing a porous matrix consisting of individual spheres, pellets or cylindrical rods in a porous basket disposed between boiler electrodes.